Declaring it a "very, very sad day" for himself and the nation, US President Donald Trump has visited a Las Vegas hospital, in a city reeling from the worst mass killing in modern US history.

Trump met with survivors and law enforcement officials in the aftermath of a gunman killing 59 people, including himself, at a concert.

"America is truly a nation in mourning," CNN quoted Trump as saying from a press conference at the Las Vegas Metropolitan Police headquarters.

"Our souls are stricken with grief for every American who lost a husband or a wife, a mother or a father, a son or a daughter. We know that your sorrow feels endless. We stand together to help you carry your pain. You are not alone. We will never leave your side."

Source: MENA